Various binders have been proposed using different binding assemblies. Typically, a plurality of holes are punched along an edge of each sheet of paper so that metallic rods or pipes are passed through these holes for retaining the paper sheets in the binding assembly. Thus, a binding assembly typically comprises a holder base which is normally attached to the inner surface of the binding of the binder, and a pair of clamping plates attached to the holder base for holding the paper sheets from both sides. A plurality of pipes project from one of the clamping plates toward the other clamping plate, and the associated rods, projecting from the other clamping plate, are received in the pipes. Conventionally, one of the clamping plates is hinged to the holder base while the other clamping plate is detachably latched to the holder base so that sheets of paper can be added to or removed from the binder at will.
The binding assembly has been conventionally composed of stamped sheet metal, but it is more preferable to fabricate a major part of the binding assembly from plastic material for the simplification of the assembling process and for the reduction of the manufacturing cost. However, using a latching mechanism made of plastic material has never been commercially successful because plastic latching mechanisms, when used in conventional binding assemblies, are unable to withstand severe impacts that latching mechanisms are subjected to.
More recently, it has been proposed to make both clamping plates detachable so that either one of them may be selectively removed while the other one is kept hinged to the holder base. Thereby, one is allowed to file and remove paper sheets from either end, i.e., first-in first-out or last-in first-out, without being required to unnecessarily remove and replace sheets of paper.
According to such a recently proposed binding assembly, a spring-loaded latching mechanism is needed for each clamping plate, and although it is possible to latch each clamping plate onto the holder base with a single hand, it is necessary to use both hands simultaneously when unlatching the clamping plate from the holder base, one hand for unlatching the latching mechanism and the other for pulling the clamping plate away from the holder base. To avoid this inconvenience, it is possible to use a heart cam mechanism so that the latching mechanism can be latched and unlatched in an alternating fashion each time the user pushes a lever, but it complicates the latching mechanism and adds to the manufacturing cost.